Single transistor type magnetic random access memory device and method of operating and manufacturing the same

ABSTRACT

A single transistor type magnetic random access memory device and a method of operating and manufacturing the same, wherein the single transistor type magnetic random access memory device includes a substrate, first and second doped regions spaced apart from each other, a gate dielectric layer on a portion of the semiconductor substrate between the first and second doped regions, a magnetic tunnel junction on the gate dielectric layer, word lines on the magnetic tunnel junction extending in a first direction which is the same direction as the second doped region, bit lines connected to the first doped region in a second direction perpendicular to the first direction, and an insulating layer covering the gate dielectric layer, the magnetic tunnel junction, and the word lines. The single transistor type magnetic random access memory device has a simple circuit structure, has a prolonged lifetime and is easy to manufacture.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a single transistor type magneticrandom access memory device and a method of operating and manufacturingthe same. More particularly, the present invention relates to a singletransistor type magnetic random access memory device for reading currentvalues flowing through channels of a transistor having gates formed ofmagnetic tunnel junction (MTJ) cells instead of reading resistancevalues of the MTJ cells and methods of operating and manufacturing thesame.

2. Description of the Related Art

A magnetic random access memory (MRAM), which is a nonvolatile memorydevice, uses a magnetic characteristic of a material to store data. Inprinciple, the MRAM can realize both rapid reading/writing time of astatic random access memory (SRAM) and high integration density of adynamic random access memory (DRAM) and can rewrite data any time.

A conventional MRAM has a rapid rate and a low driving voltage, whichare ideal characteristics for a memory device. However, since theconventional MRAM is formed by depositing several thin films, thestructure thereof is complicated and the manufacture thereof isdifficult. Also, the conventional MRAM uses tunnel current passingthrough a tunnel barrier to read a writing state. Thus, the life of thetunnel barrier is short and an additional circuit is required to readthe tunnel current.

SUMMARY OF THE INVENTION

To solve the above-described problems, it is a first feature of anembodiment of the present invention to provide a single transistor typemagnetic random access memory device for reading tunnel current valuesflowing through channels of a transistor having gates formed of magnetictunnel junction (MTJ) cells instead of reading tunnel current flowingthrough conventional MTJ cells.

It is a second feature of an embodiment of the present invention toprovide a method of operating the single transistor type magnetic randomaccess memory device.

It is a third feature of an embodiment of the present invention toprovide a method of manufacturing the single transistor type magneticrandom access memory device.

Accordingly, to provide the first feature, there is provided a singletransistor type magnetic random access memory device. The singletransistor type magnetic random access memory device includes asubstrate, first and second doped regions which are spaced apart fromeach other and are formed by implanting dopants into the semiconductorsubstrate, a gate dielectric layer formed on a portion of thesemiconductor substrate between the first and second doped regions, anMTJ formed on the gate dielectric layer, word lines formed on the MTJextending in a first direction which is a same direction as the seconddoped region, bit lines connected to the first doped region in a seconddirection perpendicular to the first direction, and an insulating layerfor covering the gate dielectric layer, the MTJ, and the word lines toinsulate the gate dielectric layer, the MTJ, and the word lines from thebit lines, wherein the first and second doped regions, the gatedielectric layer, and the MTJ constitute a single transistor.

It is preferable that the first doped region is disconnected from afirst doped region of another transistor.

It is preferable that the word lines and the bit lines are formed ofmetal.

The single transistor type magnetic random access memory device mayfurther include the metal strapping lines which are parallel to sourcesthat are disposed parallel to the word lines and which are connected tosources in a predetermined number of memory devices.

To achieve the second feature, there is provided a method of operating asingle transistor type magnetic random access memory device. The methodincludes: (a) applying current Ix to bit lines for addressing, applyingcurrent Iy to word lines, making magnetized directions of magneticlayers of an MTJ in an anti-parallel direction, forming a resistance R₁,and writing data “1” at a selected memory cell; (b) applying current Ixto the bit lines for addressing, applying current—Iy in a directionopposite to the current Iy to the word lines, making the magnetizeddirections of the magnetic layers of the MTJ in a parallel direction,forming a resistance R₀, and writing data “0” at a selected memory cell;and (c) applying a voltage Vds to the bit lines, applying a voltage Vinto the word lines, sensing channel current flowing from a drain that isa first doped region to a source that is a second doped region, andreading the data stored at the step (a) or (b).

It is preferable that (c) is performed by detecting the channel currentvia a sense amplifier connected to the source.

In (c), the channel current may be detected from metal strapping lineswhich are parallel to sources disposed parallel to the word lines andare connected to sources in a predetermined number of memory devices.

In (c), the channel may use a depletion mode MOSFET that is doped inadvance, to precisely distinguish differences in the channel current dueto the difference between the resistances R₁ and R₀.

In (c), a pulse voltage may be applied to the word lines to read changesin the channel current due to a time delay according to the resistancesR₁ and R₀ during formation of the channel.

To provide the third feature, there is provided a method ofmanufacturing a single transistor type magnetic random access memorydevice. The method includes: (a) sequentially forming a gate dielectriclayer and MTJ forming layers on a substrate; (b) forming a firstinsulating layer to cover the resultant layers of (a) on the substrate;(c) exposing an upper portion of the MTJ; (d) forming a word line on theexposed portion of the MTJ; (e) forming a second insulating layer on thefirst insulating layer to cover the word line; (f) forming a source anda drain by implanting dopants into portions of the substrate at bothsides of the MTJ and the word line; (h) forming a third insulatinglayer, on the second insulating layer, which contacts the source and thedrain and covers the stacked layers between the source and the drain;and (i) forming a bit line, on the third insulating layer, whichcontacts the drain.

It is preferable that (a) includes patterning the layers which arestacked.

It is preferable that (d) includes patterning the word line.

It is preferable that (f) includes: (f1) patterning the first and secondinsulating layers to expose portions of the substrate at both sides ofthe gate electric layer and the MTJ; and (f2) implanting dopants intothe exposed portions of the substrate to form first and second dopedregions which are a drain and a source, respectively, and are spacedapart from each other.

It is preferable that (i) includes: (i1) patterning the third insulatinglayer to expose the drain; and (i2) forming a conductive bit line, onthe third insulating layer, which connects to the exposed drain.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will becomemore apparent by describing in detail preferred embodiments thereof withreference to the attached drawings in which:

FIG. 1 illustrates a view of a cell array of a single transistor typemagnetic random access memory device according to a preferred embodimentof the present invention;

FIG. 2 illustrates a cross-sectional view of the single transistor typemagnetic random access memory device according to a preferred embodimentof the present invention;

FIGS. 3A and 3B illustrate cross-sectional views explaining a writingoperation of the single transistor type magnetic random access memorydevice according to a preferred embodiment of the present invention;

FIG. 4 illustrates a cross-sectional view explaining a reading operationof the single transistor type magnetic random access memory deviceaccording to a preferred embodiment of the present invention;

FIG. 5 illustrates a view showing changes in an applied voltage and ameasured voltage during the reading operation of the single transistortype magnetic random access memory device according to a preferredembodiment of the present invention;

FIG. 6 illustrates a schematic plan view of a cell array of the singletransistor type magnetic random access memory device according to apreferred embodiment of the present invention;

FIG. 7 illustrates a cross-sectional view taken along line VII—VII ofFIG. 6; and

FIGS. 8A through 8H illustrate cross-sectional views explaining steps ofa method of manufacturing the single transistor type magnetic randomaccess memory device according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a single transistor type magnetic random access memorydevice and operating and manufacturing methods thereof will be describedwith reference to the attached drawings, in which:

FIG. 1 illustrates an equivalent circuit diagram of a cell array in asemiconductor chip having a memory transistor according to a preferredembodiment of the present invention. Reference numeral 10 denotes asingle memory transistor and reference numeral 30 denotes an MTJ whichwill be described later. Reference numeral B denotes bit lines forconnecting drains D of memory transistors 10 to each other and referencenumeral W denotes word lines of the memory transistors 10. Referencenumeral P denotes plate lines for straightly connecting sources S ofcells which are parallel to the word lines W. A sense amplifier S/A isconnected to the plate line P.

A cell array represents that a plurality of memory transistors 10 arearrayed lengthwise and crosswise. Thus, in the cell array, the wordlines W corresponding to the number of crosswise arrayed memorytransistors 10 and the bit lines B corresponding to the number oflengthwise arrayed memory transistors 10 are arrayed to be perpendicularto each other. The plate lines P are parallel to the word lines W asshown in FIG. 1. Each source S of each memory transistor 10 is connectedto a means for measuring current flowing through channels. Preferably,this means is the sense amplifier S/A. However, other current measuringdevices may be connected to each source S of each memory transistor 10.

FIG. 2 illustrates a cross-sectional view of a single transistor typemagnetic random access memory device according to the preferredembodiment of the present invention. Referring to FIG. 2, a memorytransistor is formed on a substrate 20. A source S and a drain D areconductive doped regions which are formed from the surface of thesubstrate 20 to a predetermined depth. The source S and the drain D arespaced apart from each other. A gate dielectric layer 22 is formed onthe surface of a portion of the substrate 20 between the source S andthe drain D. An MTJ 30 is formed on the gate dielectric layer 22. A wordline W, which extends in a first direction parallel to the source S, isformed on the MTJ 30. A bit line B, which is connected to the drain D,is formed over the word line W in a second direction perpendicular tothe word line W. An insulating layer 24 is formed between the bit line Band the sequentially stacked dielectric layer 22, the MTJ 30, and theword line W. The insulating layer 24 insulates the dielectric layer 22,the MTJ 30, and the word line W from the bit line B. The word line Wserves as a gate G shown in FIG. 1.

The MTJ 30 has a structure in which a tunnel barrier layer 34 is formedbetween two or more magnetic layers. The magnetized direction of a lowerlayer 32 of the MTJ 30 is fixed, and the magnetized direction of theupper layer 36 of the MTJ 30 becomes parallel or anti-parallel to themagnetized direction of the lower layer 32 by an applied electric field.

The drain D is disconnected from other drains to insulate cells fromeach other so that differences in current detected in a depletion mode,which will be described later, may easily be distinguished.

The word line W and the bit line B are formed of metal layers to supplycurrent sufficient for switching.

An operation of a single transistor type magnetic random memory deviceaccording to a preferred embodiment of the present invention will now bedescribed.

Writing Operation

As shown in FIG. 3A, first current Ix is applied to a bit line B foraddressing, and current Iy is applied to a word line W. Thus, directcurrent flows in a +y direction. As a result, a magnetic field is formedin a clockwise direction and thus the upper layer 36 of the MTJ 30 ismagnetized in a −x direction, i.e., a left direction in FIG. 3A. Here,if the lower layer 32 of the MTJ 30 is magnetized in an +x direction,i.e., a right direction in FIG. 3A, the magnetic layers 32 and 36 aremagnetized in anti-parallel directions as shown with arrows. Here, highresistance R₁ is formed in the MTJ 30 and data “1” is written in aselected memory cell.

A process of writing data “0” in a memory cell will be described withreference to FIG. 3B. First, for addressing, current Ix is applied to abit line B, and current−Iy in a direction opposite to the current Iy isapplied to a word line W. As a result, a magnetic field is formed in acounterclockwise direction to magnetize the upper layer 36 of the MTJ inan x direction. Here, if the magnetized direction of the MTJ 30 is the xdirection, the magnetized directions of the magnetic layers 32 and 36are in parallel. Here, low resistance R₀ is formed in the MTJ 30 anddata “0” is written in a selected memory cell.

Reading Operation

FIG. 4 illustrates a cross-sectional view for explaining a readingoperation of the memory device according to a preferred embodiment ofthe present invention. FIG. 5 illustrates a view showing changes in anapplied voltage and a measured voltage during the reading operation ofthe single transistor type magnetic random access memory deviceaccording to a preferred embodiment of the present invention.

Referring to FIGS. 4 and 5, first, a voltage Vds is applied to a bitline B. After the voltage Vds is stabilized, a voltage Vin is applied toa word line W. Then, a channel is formed between a source S and a drainD of a memory transistor. A sense amplifier S/A is connected to thesource S to detect channel current Ids from the source S. The channelcurrent Ids varies depending on resistances R₁ and R₀ of the MTJ 30 andthus “1” and “0” are distinguished from the channel current Ids. Here, adepletion mode transistor, in which a channel is doped in advance, maybe used to precisely distinguish channel current values.

Due to the application of the voltage Vin to the word line W, a gatevoltage Vg, which is delayed by a time constant τ, which is determinedby the product of the resistances R₁ and R₀ of the MTJ 30 and gatecapacitance (Cg), is applied to the gate dielectric layer 22. Thus, asshown in FIG. 5, resistance states of the MTJ 30 are distinguished byusing different times for forming a channel according to the strength ofthe resistances R₁ and R₀ of the MTJ 30. As a result, it is possible toread data stored in a memory cell. In other words, channel current Ids,which is delayed by a time constant τ′, or an integral value of thechannel current Ids is read at a predetermined time starting after thevoltage Vin is applied to the word line W to distinguish a resistancestate R₁ or R₀. Also, channel current values may vary after the channelis formed. Thus, R₁ and R₀ values are distinguished by measuring thechannel current values after the channel is formed.

The source S has a high resistance and thus a high-speed operation maybe difficult in the source S. To solve this problem, as shown in FIGS. 6and 7, metal strapping lines T which are low resistance lines aredisposed parallel to the high resistance lines that are sources S. Next,the strapping lines T between bit lines in a predetermined number ofmemory devices are connected to the high resistance lines that aresources S under the strapping lines T. As a result, a time delay may bereduced. Reference numeral T′ shown in FIGS. 6 and 7 denotes a contactsurface between a source S and a strapping line T.

FIGS. 8A through 8H illustrate cross-sectional views for explaining amethod of manufacturing the memory device of the present invention. Likereference numerals in the drawings denote like members, and theirdetailed description will be omitted.

As shown in FIG. 8A, a gate dielectric layer 22 and an MTJ 30 aresequentially formed on a semiconductor substrate 20.

The stacked layers on the substrate 20 are patterned as shown in FIG.8B.

Then, a first insulating layer 24 a is formed to cover the patternedlayers on the substrate as shown in FIG. 8C.

Thereafter, the first insulating layer 24 a is patterned to expose anupper central portion of the MTJ 30, and a conductive word line W isformed on the exposed portion of the MTJ 30 and portions of the firstinsulating layer 24 a. Next, the word line W is patterned as shown inFIG. 8D.

A second insulating layer 24 b is formed on the first insulating layer24 a to cover the word line W as shown in FIG. 8E.

Then, the first and second insulating layers 24 a and 24 b are patternedso that portions of the substrate 20 at both sides of the stacked layersof the gate dielectric layer 22 and the MTJ 30 are exposed as shown inFIG. 8F.

Thereafter, dopants are implanted into the exposed portions of thesemiconductor substrate 20 to form a first doped region and a seconddoped region which are a drain D and a source S, respectively, and arespaced apart from each other, as shown in FIG. 8F.

Next, a third insulating layer 24 c is formed on the second insulatinglayer 24 b to contact the source S and the drain D and cover the stackedlayers between the source S and the drain D as shown in FIG. 8G.

Then, the third insulating layer 24 c is patterned to expose a portionof the drain D. Next, a conductive bit line B is formed to be connectedto the exposed portion of the drain D, as shown in FIG. 8H. Theconductive bit line B connects exposed portions of the plurality ofdrains D, in the cell array of FIGS. 1 and 6, to each other.

As described above, a single transistor type magnetic random accessmemory device has a simple circuit structure. Thus, it is easy tomanufacture the single transistor type magnetic random access memorydevice having a highly integrated structure. Also, the life of thesingle transistor type random access memory device may be prolonged.

Preferred embodiments of the present invention have been disclosedherein and, although specific terms are employed, they are used and areto be interpreted in a generic and descriptive sense only and not forthe purpose of limitation. The drawings referred to herein to describethe preferred embodiments of the present invention are used forillustration purposes only, and not for the purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the invention as set forth in the followingclaims

What is claimed is:
 1. A single transistor type magnetic random accessmemory device comprising: a substrate; first and second doped regionswhich are spaced apart from each other and are formed by implantingdopants into the semiconductor substrate; a gate dielectric layer formedon a portion of the semiconductor substrate between the first and seconddoped regions; a magnetic tunnel junction formed on the gate dielectriclayer; word lines formed on the magnetic tunnel junction and extendingin a first direction which is a same direction as the second dopedregion; bit lines connected to the first doped region in a seconddirection perpendicular to the first direction; an insulating layer forcovering the gate dielectric layer, the magnetic tunnel junction, andthe word lines to insulate the gate dielectric layer, the magnetictunnel junction, and the word lines from the bit lines; and metalstrapping lines which are parallel to sources disposed parallel to theword lines and are connected to sources in a predetermined number ofmemory devices, wherein the first and second doped regions, the gatedielectric layer, and the magnetic tunnel junction constitute a singletransistor.
 2. The single transistor type magnetic random access memorydevice as claimed in claim 1, wherein the first doped region isdisconnected from a first doped region of another transistor.
 3. Thesingle transistor type magnetic random access memory device as claimedin claim 1, wherein the word lines and the bit lines are formed ofmetal.